Universal pneumatic ventricular assist device

ABSTRACT

A pneumatic ventricular assist device is designed for use in any circulatory support application including RVAD, LAVD, or BIVAD, trans-operative, short-term or long-term, tethered implantable or extracorporeal. It consists of a soft contoured pumping shell and a disposable pumping unit, which includes a pump sac, two one-way valves, and tubing connectors. The pumping unit is specially designed to allow continuous and fluid movement of blood and to limit blood-contacting surfaces, and is made of a supple and elastic material such as silicone. The components can be inexpensively and reliably manufactured by injection molding. Also, the pumping shell and pumping unit include complementary features that quickly and securely hold the pumping unit, and any attached cannulae, in place.

[0001] This application claims priority from a Provisional Application,Serial No. 60/475,062, filed May 30, 2003.

FIELD OF THE INVENTION

[0002] The present invention relates to blood pumping devices, and, moreparticularly, to ventricular assist devices.

BACKGROUND

[0003] A ventricular assist device (“VAD”) is used to help supplementthe heart's pumping action both during and after certain kinds ofsurgery, in situations where a complete cardiopulmonary bypass (using aheart-lung machine) is neither needed nor advisable in light of theserious side effects associated therewith. Ventricular assist devicestypically comprise a pair of cannulae or other tubing and some sort ofpump operably connected to the cannulae. In use, the cannulae areattached to either the left side of the heart (a left ventricular assistdevice) or to the right side of the heart (a right ventricular assistdevice) “in parallel,” i.e., the pump supplements the heart's pumpingaction but does not completely bypass it, and the pump is activated.Alternatively, a pump may be directly implanted into the body.

[0004] Originally, ventricular assist devices were air powered, whereinfluctuating air pressure, provided by a simple mechanical air pumpmachine, was applied to a bladder-like sac. The bladder had input andoutput valves, so that blood would enter the bladder through the inputvalve when the pressure on the bladder was low, and exit the bladderthrough the output valve when the pressure on the bladder was high.Unfortunately, these pneumatic ventricular assist devices werecomplicated, and used expensive mechanical valves that were prone tofailure, subject to “clogging,” and that caused blood trauma or damagebecause of hard, metal edges and the like.

[0005] To overcome these problems, other types of ventricular assistdevices were developed, including axial flow pumps for temporaryinsertion directly into the heart, and centrifugal pumps. The former arebased on the Archymides' Principle, where a rod with helical blades isrotated inside a tube to displace liquid. In use, a catheter-mounted,miniature axial flow pump is appropriately positioned inside the heart,and is caused to operate via some sort of external magnetic drive orother appropriate mechanism. With high enough RPM's, a significantamount of blood can be pumped. In the case of centrifugal pumps, bloodis moved by the action of a rapidly rotating impeller (spinning cone orthe like), which causes the blood to accelerate out an exit. Both ofthese categories of ventricular assist devices are generally reliableand implantable, but are very expensive, not particularly durable, andare not useful in situations where a patient needs a true pulsatingblood supply. Specifically, axial and centrifugal pumps are typicallyleft on in a continuous operation mode, where a steady stream of bloodis supplied on a continuous basis, as opposed to the natural rhythm ofthe heart, which acts on a periodic, pulse-producing basis. In addition,such pumps are still largely in the developmental or trial phase.

[0006] Accordingly, a primary object of the present invention is toprovide a pneumatic ventricular assist device that offers the advantagesof pneumatic operation without the drawbacks associated with priorpneumatic devices.

SUMMARY

[0007] A pneumatic ventricular assist device (“VAD”) is for use in anycirculatory support application including RVAD, LAVD, or BIVAD,trans-operative, short-term or long-term, tethered implantable orextracorporeal. The VAD comprises a soft-contoured (rounded,low-profile) pumping shell and a disposable pumping unit that includes ablood sac, two one-way valves, and two tubing connectors. The pumpingunit is specially designed to allow continuous and fluid movement ofblood and to limit blood-contacting surfaces, and is made of a suppleand elastic material such as silicone. The components can beinexpensively and reliably manufactured by injection molding. Also, thedesign of the VAD, according to the present invention, facilitatespriming, de-bubbling, and connection to the body.

[0008] For assembly, the pumping shell is opened (it includes two halvesin a clam shell-like arrangement), the pumping unit is positionedinside, and the shell is closed. The interior of the shell iscomplementary in shape to the pumping unit: a pumping chamber portionholds the blood sac, and two pump inlets are shaped to securely hold thevalves and tubing connectors. A disposable seal rests between the twoclamshell halves for sealing the connection there between.

[0009] In use, the VAD is connected to a patient's heart by way of twocannulae connected to the tubing connectors (the cannulae are connectedto the heart at appropriate locations according to standard surgicalpractices). Then, a pneumatic drive unit is attached to an air inlet inthe pumping shell by way of an air line or the like. Subsequently, thedrive unit is activated to cause the blood sac to move in and out, in agentle pumping action, by way of controlled periodic air pressureintroduced into the pumping shell through the air inlet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] These and other features, aspects, and advantages of the presentinvention will become better understood with respect to the followingdescription, appended claims, and accompanying drawings, in which:

[0011]FIG. 1 is a perspective exploded view of a universal pneumaticventricular assist device according to the present invention;

[0012]FIG. 2 is a perspective exploded view of the ventricular assistdevice with an assembled disposable pump assembly;

[0013]FIG. 3 is a perspective, partially exploded view of theventricular assist device in place against a lower half of a pumpingshell portion of the ventricular assist device;

[0014]FIG. 4A is a elevation cross-sectional view of a valve portion ofthe ventricular assist device, taken along line 4A-4A in FIG. 1;

[0015]FIG. 4B is a perspective cross-sectional view of the valve portionof the ventricular assist device shown in FIG. 4A;

[0016]FIG. 5A is a plan view of a disposable pump blood sac portion ofthe ventricular assist device;

[0017]FIG. 5B is a cross-sectional view of the disposable blood sactaken along line 5B-5B in FIG. 5A;

[0018]FIGS. 6A-6C show various elevation views of how the ventricularassist device is placed and connected for use with a patient; and

[0019]FIG. 7 is a perspective view of two of the ventricular assistdevices in use extracorporeally with a patient.

DETAILED DESCRIPTION

[0020] With reference to FIGS. 1-7, a ventricular assist device (VAD) 10includes: a reusable pumping shell 12 having a first or upper“clamshell” half 14 and a second or lower clamshell half 16 removablyattachable to the first half 14; a disposable seal 18 that fits betweenthe two pumping shell halves 14, 16; and a disposable pumping unit 20that includes: a disposable blood sac 22 that fits in the pumping shell12; two disposable, one-way injection-molded valves 24, 26 attached tothe blood sac 22; and two tubing connectors 28, 30 attached to thevalves. Although the valves 24, 26 are identical, one valve 26 ispositioned to act as an inlet valve, and the other valve 24 ispositioned to act as an outlet valve (i.e., blood can only flow throughthe valves 24, 26 as indicated by the arrows in FIG. 3).

[0021] For assembly, the disposable pumping unit 20 is placed againstthe lower pumping shell half 16, the seal 18 is positioned in place, andthe upper pumping shell half 14 is placed against and connected to thelower pumping shell half 16 (by way of screws or other fasteners). Inuse, the ventricular assist device 10 is appropriately connected to apatient's heart by way of a ventricular (or atrial) cannula 32 and anarterial cannula 34 respectively connected to the tubing connectors 28,30. Then, a pneumatic drive unit 36 is operably attached to an air inlet38 in the ventricular assist device 10 by a pneumatic line 40 or thelike (see FIG. 7). Subsequently, the drive unit 36 is activated to causea portion of the disposable blood sac 22 to move in and out, in a gentlepumping action, by way of controlled fluctuating air pressure introducedinto the pumping shell 12 through the air inlet 38.

[0022] The pumping shell 12 is either molded or machined from a hardmaterial that may or may not be implantable in the human body, and mayor may not be reusable. The pumping shell 12 comprises the two halves14, 16 (generally similar to one another), which mate together like aclamshell and together define a rounded pumping chamber 42 and twogenerally cylindrical pump inlets 44, 46 into the pumping chamber. Asbest seen in FIGS. 2 and 3, the pump inlets 44, 46 are provided withannular contours or shoulders 37 for holding the connectors 28, 30(i.e., each pump shell half includes a semi-annular shoulder which, whenthe two halves are connected, together define an annular shoulder). Inaddition, the lower shell half 16 includes the air inlet 38, which is asmall hole or channel extending from the outer surface of the shellthrough the shell wall to the pumping chamber 42. The outer surfaces ofthe shell halves 14, 16 are rounded, while the peripheral inner surfacesare flat so that the shell halves fit snugly against one another. Theshape of the pumping shell is generally flat and softly contoured (i.e.,rounded, ellipsoidal) so that it may be comfortably implanted.

[0023] As mentioned, the pumping shell pump inlets 44, 46 are generallycylindrical and dimensioned to hold and support the entireties of thecylindrical valves 24, 26 therein. As should be appreciated, having thevalves enclosed within the confines of the complementary-shaped pumpinlets maximizes support of the valves, thereby enhancing theirperformance and durability. It also reduces the likelihood of the valvesbecoming dislodged or loose during use.

[0024] The blood sac 22, valves 24, 26, and cannulae 32, 34 arespecially designed to allow continuous and fluid motion of blood and tolimit blood contacting surfaces. These components are made of a suppleelastomer such as silicone that will stretch and deform to pressuregradients reducing the damage to blood cells. With reference to FIGS. 4Aand 4B, the valves 24, 26 are hinge-less and have valve leaflet portions50 that are flexible and elastic, simulating the action of natural heartvalves, and improving their reliability and durability. The valves areinjection molded in four piece molds reducing the manufacturing costcompared to biological or mechanical valves. In use, blood can flowthrough the valves in one direction only, from the valve inlet 52 to thevalve outlet 54, i.e., in the direction of the arrows in the figures.Specifically, when the pressure is greater on the valve inlet side 52,the valve leaflets 50 respectively flex upwards and downwards, allowingblood to pass. However, when the pressure is greater on the valve outletside 54, the leaflets are gently but forcibly compressed together,preventing blood from flowing back through the valve. Because the valvesare each one-piece, are made from silicone (or another suitablematerial), and have rounded or contoured inner surfaces, they are veryreliable, perform well, and minimize damage to blood. For example, asshown in FIG. 4B, note that the valve wall 53 leading up to theleaftlets 50 is rounded/sloped to minimize blood disturbance.

[0025] As indicated in FIG. 4A, the sac 22 and connectors 28 areconfigured to fit within the entrance and exit ends of the valves 24, 26and against interior, circumferential shoulders 55 provided in thevalves. This produces a continuous surface between the various elementsand eliminates any sharp lips or ridges in the blood flow path, reducingblood damage.

[0026]FIGS. 5A and 5B (in addition to FIGS. 1-3) show the pumping sac22. The pumping sac is bilaterally symmetric and includescircular/tubular inlets 70, 72 connected to a main pumping chamber 73.The pumping chamber 73 sports a gently rounded or circular profile,which has been found to maximize pumping effectiveness and to reduceblood trauma during the pumping action. More specifically, the pumpingchamber 73 is generally shaped like a semi-flattened ellipsoid, i.e.,flat, circular top and bottom walls 74 a, 74 b interconnected by arounded sidewall 75.

[0027] The blood sac, valves, and/or cannulae may be coated withlubricant, hydrophobic, antibacterial and/or antithrombotic coatings,including but not limited to PTFE coatings, heparin bonded coatings,fluorinated coatings, treclosan and silver compound coatings, andanti-calcification agent releasing coatings such as previously describedto improve blood compatibility and non thrombogenicity.

[0028] The connectors 28, 30 are made of a hard material (e.g., plastic,stainless steel, titanium), molded or machined, that will secure theconnection between the valves 24, 26 and the cannulae 32, 34. The tubingconnectors 28, 30 each include a cylindrical through-bore, a cylindricalfore-portion that fits into the valves 24, 26, an annular flange 76which corresponds in shape to the pump inlet shoulders 37, and arear-portion dimensioned to accommodate a cannula. In use, when thepumping unit 20 is placed in the pumping shell 12, the valves' annularflanges 76 lie against the pump inlet shoulders, securely holding thetubing connectors 28, 30 in place and preventing their removal from thepumping shell.

[0029] The seal 18 is made of a soft elastomer like the pumping sac andvalves, but will not be in contact with blood and is only used to insurean airtight fit of the pumping shell halves 14, 16. The disposablepumping unit 20 (blood sac, valves and connectors and seal) may bepreassembled and coated as a single disposable part.

[0030] To ensure that the cannulae 32, 34 remain securely connected tothe connectors 28, 30, the inlet portions 44, 46 of each pumping shellhalf are provided with protruding, semi-annular gripping ridges 60 (seeFIG. 2). In use, when the pumping unit 20 is placed in the lower pumpingshell half 16, as shown in FIG. 3, the cannulae 32, 34 contact thegripping ridges of the lower half 16. Then, when the upper half 14 isplaced against and connected to the lower half 16, the gripping ridges60 of both halves bite into and engage the cannulae, securing them inplace.

[0031] The whole system has been designed to be used in a wide range ofapplications of circulatory support, by simply selecting the appropriatecannulae and accessories. Intended applications include short termtrans-operative support (a few hours), acute and post-cardiotomy support(up to a couple of weeks), bridge to transplant (˜3-6 months), bridge torecovery (˜several years) and destination therapy (until death). Thedevice is also designed to be used as either a right VAD (FIG. 6B), aleft VAD (FIG. 6A), or for bi-ventricular use (FIG. 6C), and to be usedas a tethered implant(s), paracorporealy, or extracorporealy (FIG. 7).

[0032] To install the system, first the cannulae are sewn to the atrium,ventricle or outflowing artery of the compromised side of the heart, asapplicable. The cannulae are then connected to the disposable pumpingunit 20, while carefully removing any air bubbles in the system. Theblood sac assembly is supple and flexible, facilitating its priming andde-bubbling. The connectors 28, 30 are also made to be easily connectedand disconnected, facilitating this procedure. Once the system has beenproperly purged and connected, the pumping shell 12 is locked closedover the pumping unit. The blood sac assembly is symmetrical so that itcan be placed either with the inflow valve on the left or on the right,making its design more adaptable to different applications. Theconnectors fit inside the pumping shell so that when the latter isclosed it will crimp down on the cannulae connections preventing anaccidental disconnection, as mentioned above. The device can then beplaced in the abdomen or outside the body and the drive unit can beactivated to start pumping.

[0033] Although the ventricular assist device of the present inventionhas been illustrated as having a pumping shell with two separate halves14, 16, the halves could be hinged together or otherwise permanentlyconnected without departing from the spirit and scope of the invention.Also, although the pumping unit has been described as comprisingseparate components connected together, the pumping unit could beprovided as a single unit, i.e., a unitary piece of molded silicone.This also applies to the valves 24, 26 and connectors 28, 30, i.e., theconnectors could be provided as part of the valves.

[0034] Although the valves 24, 26 have been characterized as beingidentical and each having two leaflets, it should be appreciated thatthe valves 24, 26 could have a different number of leaflets, e.g., 1leaflet, or 3 leaflets, and the two valves 24, 26 could be differentfrom one another. More specifically, where operating pressures on thetwo valves may be different (because one is acting as an inlet valve andthe other acting as an outlet valve), it may be advantageous to utilizevalves with different characteristics.

[0035] Since certain changes may be made in the above-describeduniversal pneumatic ventricular assist device, without departing fromthe spirit and scope of the invention herein involved, it is intendedthat all of the subject matter of the above description or shown in theaccompanying drawings shall be interpreted merely as examplesillustrating the inventive concept herein and shall not be construed aslimiting the invention.

Having thus described the invention, what is claimed is:
 1. A pneumatic ventricular assist device comprising: a. a pumping shell comprising an upper pumping shell half and a lower pumping shell half, wherein: the upper and lower pumping shell halves are configured to fit against one another to together define a rounded, interior pumping chamber and two generally-cylindrical pump inlets extending from the pumping chamber to the pumping shell exterior; and the pumping shell includes an air inlet extending from the pumping shell exterior through to the pumping chamber; and b. a pumping unit comprising: i. a flexible blood sac configured to reside in the pumping chamber and having an interior and first and second tubular inlets; ii. first and second one-way valves dimensioned to fit in the pumping shell pump inlets and respectively connected to the first and second tubular inlets of the blood sac, said valves including tubular inlets and outlets each with an outwards-facing annular shoulder, wherein end portions of the blood sac tubular inlets fit inside the valve inlets and outlets and against the annular shoulders thereof to form a substantially-continuous internal surface between the blood sac interior and valve inlets and outlets for minimizing blood trauma; and iii. first and second tubing connectors dimensioned to at least partially fit in the pumping shell pump inlets and respectively connected to the first and second valves, said tubing connectors each having an annular flange, wherein the tubing connectors include cylindrical fore portions that fit inside the valve inlets and outlets and against the annular shoulders thereof to form respective substantially-continuous internal surfaces between the tubing connector interiors and valve inlets and outlets for minimizing blood trauma; c. wherein the pumping shell pump inlets each include: (i) an annular, inwards-facing shoulder against which the annular flange portions of the tubing connectors respectively rest to hold the tubing connectors in place; and (ii) an annular gripping ridge for securing cannulae connected to the tubing connectors in place when the pumping shell halves are connected together.
 2. The pneumatic ventricular assist device of claim 1 wherein the pumping shell has a rounded, generally-flattened, ellipsoid-shaped outer surface for facilitating implantation.
 3. The pneumatic ventricular assist device of claim 1 wherein the first and second one-way valves are flexible, one-piece, hinge-less valves each having two flexible valve leaflet portions separating the valve inlet and outlet, wherein the leaflet portions: (i) compress together, preventing blood from flowing back through the valve, when blood pressure is greater on the valve outlet side than on the valve inlet side; and (ii) flex outwards, allowing blood to pass through the valve, when blood pressure is greater on the valve inlet side than on the valve outlet side.
 4. A pneumatic ventricular assist device comprising: a. a pumping shell having two pumping shell halves that together define an interior pumping chamber and two pump inlets when connected; and b. a pumping unit comprising: a flexible blood sac configured to reside in the pumping chamber and having first and second sac inlets; first and second one-way valves dimensioned to fit in the pumping shell pump inlets and respectively connected to the first and second sac inlets; and first and second tubing connectors dimensioned to at least partially fit in the pumping shell pump inlets and respectively connected to the first and second valves; c. wherein the pumping shell pump inlets each include an annular gripping ridge for securing cannulae connected to the tubing connectors in place when the pumping shell halves are connected together.
 5. The pneumatic ventricular assist device of claim 4 wherein the pumping shell pump inlets each include an annular, inwards-facing shoulder against which annular flange portions of the tubing connectors respectively rest to hold the tubing connectors in place.
 6. The pneumatic ventricular assist device of claim 4 wherein the pumping shell has a rounded, generally-flattened, ellipsoid-shaped outer surface for facilitating implantation.
 7. The pneumatic ventricular assist device of claim 4 wherein the first and second one-way valves are one-piece, hinge-less valves each having a valve inlet side, a valve outlet side, and two flexible valve leaflet portions separating the valve inlet and outlet sides, wherein the leaflet portions: (i) compress together, preventing blood from flowing back through the valve, when blood pressure is greater on the valve outlet side than on the valve inlet side; and (ii) flex outwards, allowing blood to pass through the valve, when blood pressure is greater on the valve inlet side than on the valve outlet side.
 8. A pneumatic ventricular assist device comprising: a. a pumping shell having an interior pumping chamber and two pump inlets; and b. a pumping unit comprising: a flexible blood sac configured to reside in the pumping chamber and having first and second sac inlets; first and second one-way valves dimensioned to fit in the pumping shell pump inlets and respectively connected to the first and second sac inlets; and first and second tubing connectors dimensioned to at least partially fit in the pumping shell pump inlets and respectively connected to the first and second valves; c. wherein the pumping shell pump inlets each include an annular, inwards-facing shoulder against which annular flange portions of the tubing connectors respectively rest to hold the tubing connectors in place.
 9. The pneumatic ventricular assist device of claim 8 wherein: the pumping shell comprises two pumping shell halves that together define the interior pumping chamber and two pump inlets when connected; and the pumping shell pump inlets each include an annular gripping ridge for securing cannulae connected to the tubing connectors in place when the pumping shell halves are connected together.
 10. The pneumatic ventricular assist device of claim 8 wherein the pumping shell has a rounded, generally-flattened, ellipsoid-shaped outer surface for facilitating implantation.
 11. The pneumatic ventricular assist device of claim 8 wherein the first and second one-way valves are one-piece, hinge-less valves each having a valve inlet side, a valve outlet side, and two flexible valve leaflet portions separating the valve inlet and outlet sides, wherein the leaflet portions: (i) compress together, preventing blood from flowing back through the valve, when blood pressure is greater on the valve outlet side than on the valve inlet side; and (ii) flex outwards, allowing blood to pass through the valve, when blood pressure is greater on the valve inlet side than on the valve outlet side.
 12. A pneumatic ventricular assist device comprising: a. a pumping shell having an interior pumping chamber and two pump inlets; and b. a pumping unit comprising: i. a flexible blood sac configured to reside in the pumping chamber and having an interior and first and second inlets into the sac interior; ii. first and second generally-cylindrical, one-way valves dimensioned to fit in the pumping shell pump inlets and respectively connected to the first and second sac inlets, said first and second valves each having a tubular inlet with an outwards-facing annular shoulder and a tubular outlet with an outwards-facing annular shoulder, wherein end portions of the blood sac inlets fit inside the valve inlets and outlets and against the annular shoulders thereof to form a substantially-continuous internal surface between the blood sac interior and valve inlets and outlets for minimizing blood trauma; and iii. first and second tubing connectors dimensioned to at least partially fit in the pumping shell pump inlets and respectively connected to the first and second valves, wherein the tubing connectors include cylindrical fore portions that fit inside the valve inlets and outlets and against the annular shoulders thereof to form respective substantially-continuous internal surfaces between the tubing connector interiors and valve inlets and outlets for minimizing blood trauma.
 13. The pneumatic ventricular assist device of claim 12 wherein the pumping shell pump inlets each include an annular, inwards-facing shoulder against which annular flange portions of the tubing connectors respectively rest to hold the tubing connectors in place.
 14. The pneumatic ventricular assist device of claim 12 wherein: the pumping shell comprises two pumping shell halves that together define the interior pumping chamber and two pump inlets when connected; and the pumping shell pump inlets each include an annular gripping ridge for securing cannulae connected to the tubing connectors in place when the pumping shell halves are connected together.
 15. The pneumatic ventricular assist device of claim 12 wherein the pumping shell has a rounded, generally-flattened, ellipsoid-shaped outer surface for facilitating implantation.
 16. A pneumatic ventricular assist device comprising: a. a pumping shell comprising a first pumping shell half and a second pumping shell half that fit together to define an interior pumping chamber and two elongated, generally-cylindrical pump inlets; and b. a pumping unit comprising: i. a flexible blood sac dimensioned to fit in the pumping shell and having an interior and two tubular inlets; ii. two flexible, one-piece, one-way, hinge-less valves respectively connected to the blood sac inlets, wherein the valves have cylindrical outer surfaces and are dimensioned to fit entirely within and against the elongated pump inlets for enhancing support of the valves and preventing their removal or dislodgement from the pumping shell during use of the pneumatic ventricular assist device; and iii. two tubing connectors respectively connected to the two valves and dimensioned to fit at least partially in the pumping shell pump inlets.
 17. The pneumatic ventricular assist device of claim 16 wherein the pumping shell pump inlets include inwards-facing, annular shoulders against which annular flange portions of the tubing connectors respectively rest to hold the tubing connectors in place.
 18. The pneumatic ventricular assist device of claim 16 wherein the pumping shell pump inlets include annular gripping ridge for securing cannulae connected to the tubing connectors in place when the first pumping shell half and second pumping shell half are fit together.
 19. The pneumatic ventricular assist device of claim 16 wherein: the pumping shell pump inlets include inwards-facing, annular shoulders against which annular flange portions of the tubing connectors respectively rest to hold the tubing connectors in place; and the pumping shell pump inlets include annular gripping ridge for securing cannulae connected to the tubing connectors in place when the first pumping shell half and second pumping shell half are fit together.
 20. A disposable pumping unit for a pneumatic ventricular assist device, said pumping unit comprising: a. a flexible blood sac having an interior and first and second tubular sac inlets; b. a first cylindrical-shaped, one-way valve having a tubular inlet side with an outwards-facing, annular shoulder and a tubular outlet side with an outwards-facing, annular shoulder, wherein: the outlet side of the first valve is connected to the first tubular sac inlet; and the first tubular sac inlet abuts the annular shoulder of the outlet side of the first valve to form a substantially-continuous internal surface between the first tubular sac inlet and the interior of the outlet side of the first valve; c. a first tubing connector having a tubular fore-portion connected to the tubular inlet side of the first valve, wherein the tubular fore-portion of the first tubing connector abuts the annular shoulder of the inlet side of the first valve to form a substantially-continuous internal surface between the interior of the inlet side of the first valve and the interior of the first tubing connector; d. a second cylindrical-shaped, one-way valve having a tubular inlet side with an outwards-facing, annular shoulder and a tubular outlet side with an outwards-facing, annular shoulder, wherein: the inlet side of the second valve is connected to the second tubular sac inlet; and the second tubular sac inlet abuts the annular shoulder of the inlet side of the second valve to form a substantially-continuous internal surface between the second tubular sac inlet and the interior of the inlet side of the second valve, to minimize trauma of blood passing through the pumping unit; and e. a second tubing connector having a tubular fore-portion connected to the tubular outlet side of the second valve, wherein the tubular fore-portion of the second tubing connector abuts the annular shoulder of the outlet side of the second valve to form a substantially-continuous internal surface between the interior of the outlet side of the second valve and the interior of the second tubing connector, to minimize trauma of blood passing through the pumping unit. 